Applicant""s earlier U.S. Pat. No. 6,519,033 describes a system for identifying particles in a fluid, such as microorganisms in water. The technique includes directing a narrow laser or other light beam through the fluid. The technique also includes detecting light scattered from a particular location, called a detect zone lying along the laser beam, to each of multiple detectors, when a particle passes through the detect zone. The passage of a particle through the detect zone: is an event, and the outputs of the multiple detectors upon the occurrence of an event, is called an eventvector. Applicant first programs a computer by obtaining eventvectors for each of a plurality of different species of microorganisms of interest. For each species, this is accomplished by passing particles all of a particular known species through the device and detecting the eventvectors for particles of that known species. The multiple eventvectors for each species are contained in a memory and are analyzed by an algorithm that views the particles in multi-dimensional space, in a direction that results in the closest grouping of eventvectors of the same species and greatest separation of groups of eventvectors of different species. Many of the known species will be pathogenic organisms that will be encountered in significant numbers only in an unusual situation, as when a water treatment plant is not operating properly. The system will generate an alarm signal if a significant number of particles of a known pathogenic species is detected.
When monitoring a fluid such as water in a water treatment plant, there will be particles that do not fall into any one of the known-species whose eventvectors have been entered into the computer memory. Such particles may be particles of minerals, waste, etc. However, it is possible for a significant number of particles of a new pathogenic microorganism to be accidentally or deliberately introduced into the water supply, where multiple eventvectors of the new species have not previously been entered into the computer. It is highly desirable that the particle identification system automatically generate a signal to warn personnel of the possibility that a new species of microorganism has been introduced in significant numbers in the water supply.
A system that monitors fluids such as water, for the presence of possibly harmful microorganisms or other microscopic particles, which was sensitiva to the introduction of significant numbers of particles of a new species, would be of value.
In accordance with one embodiment of the present invention, a method and apparatus are provided for identifying clusters of a new species of microorganism in a fluid, by the analysis of light scatter patterns created by particles passing through a detect zone. The outputs of a plurality of photodetectors, when a particle passes through the detect zone and scatters light towards the photodetectors, is an eventvector. After a large number of eventvectors have been detected for a quantity of water, a computer determines the locations in a multi-dimensional projection of the eventvectors, of any clusters of eventvectors that lie outside the known-particle volumes. Upon the detection of a cluster, the computer generates an alert signal that can alert responsible personnel that a new cluster has been found.
In order to increase the accuracy of the system and decrease false alarms, a background signature of the water supply in a recent safe condition, is entered into the computer. The background signature contains multiple eventvectors for recent safe water that is similar to water now being monitored. The safety can be determined by persons drinking the water and not becoming sick over a period of a day or two. The computer then compares the eventvectors generated when a new sample of water is being monitored, to the background signature earlier provided for recently interrogated similar water that has been deemed to be safe. A considerable variance in the eventvectors for the new sample compared to the previous safe sample of water, and particularly the presence of a cluster not present in the background signature of the safe water, causes the computer to generate a signal indicating that a new species of particles has been detected. A cluster can be identified by a higher density of eventvectors in the multi-dimensional space in which the eventvectors are located in the computer.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.